The invention relates to an earthing bond seal for creating an effective seal between an earthing bond and a substrate to which the earthing bond is to be electrically connected.
Electrical equipment used in many different industries must be earthed, including for example, communications equipment on aircraft or signaling equipment on railways. This typically requires each item of equipment to be electrically connected by means of metal braids or earthing wires to a painted substrate such as the frame of the aircraft. The ends of the metal braids or wires are received in terminals which are fixed to the substrate.
Fixing a terminal to a substrate may typically be carried out by means of a screw and a nut, the terminal being held tightly between the head of the screw and a surface of the substrate. In order to ensure good electrical contact between the terminal and the substrate, the surface of the substrate must be stripped of paint or other coating before the assembly of the screw and the nut. Once the assembly has been carried out, the stripped region of the support must be protected against corrosion. For the assembly of the screw and the nut, access is required to the two sides of the substrate during assembly.
EP 1 376 766 in the name of the applicant discloses a device for fixing an electrical connection terminal to a substrate. The device comprises a ring which is to be introduced into a cylindrical hole formed in the substrate, a socket for insertion into the ring and a screw for engagement with a threaded opening provided in the socket. When assembling the device, the ring is first positioned in the cylindrical hole in the substrate, and then a tensile force is exerted on the socket using a tool so as to introduce the socket into the ring with force, thereby causing radial expansion of the ring and locking of the ring in the hole. The screw is then screwed into the threaded opening in the socket, the terminal being held tightly between the head of the screw and the ring, thus making it possible to fix the terminal to the substrate and to establish electrical contact between the terminal and the substrate.
An advantage of this earthing bond is that it does not necessarily require the surface of the substrate to be stripped beforehand in order to ensure good electrical contact between the terminal and the substrate. This is because the electrical contact is produced between the ring and the inner surface of the cylindrical hole which is made in the substrate. A further advantage with this earthing bond is that it may be assembled without requiring both sides of the substrate to be accessible.
However, the integrity of such a device can be affected by the paint or other coating applied to the substrate. If the paint is applied to the substrate before the hole is drilled, paint in the vicinity of the hole may crack during or following the drilling process. This cracked paint leads to an uneven surface immediately surrounding the hole which affects the integrity of the seal formed between the earthing bond and the substrate. For instance, a poor seal could lead to corrosion of parts of the substrate exposed by the cracked paint. Sometimes the substrate may be painted subsequent to attaching the earthing bond to the substrate, but then it is difficult to prevent the ingress of paint in and around the earthing bond.
It is an object of the present invention to overcome the above noted problems by providing a seal which allows the earthing bond to be installed before or after the substrate is painted.